1. Field of the Invention
This invention relates to a method of incinerating dewatered sludge obtained by dewatering excess sludge resulting from sewage treated by the activated sludge method. More particularly, the invention relates to a method of incinerating dewatered sludge wherein the dewatered sludge is dry-distilled in a non-oxidizing atmosphere and gasified and the resulting gases are used as a heat source for drying the sludge and for other purposes. And further, this invention relates to an apparatus for dry-distilling sludge and gasifying the resulting dry-distillation residue consisting primarily fixed carbon.
2. Description of Prior Art
Sludge originating from final treatment of sewage and human waste has in most cases been disposed of by being buried in the ground or being dumped in the sea after being dewatered to a certain water content. But these days, ground in which to bury the sludge is difficult to find, and the buried sludge can cause secondary pollution or the dumped sludge can pollute the ocean. So, sludge today is primarily disposed of by incineration. In addition, to prevent the formation of hexavalent chromium compounds due to burning as well as secondary pollution, from the formation of NOx and SOx in the burnt gas caused by combustion gas, several methods (See Japanese Patent Public Disclosure (KOKAI) Nos. 98144/1976 and 36574/1977.) are currently in use for dry-distillation of the sludge.
Sludge is difficult to dewater, and efficient, or economical dewatering with the dewatering apparatus generally produces the sludge which usually contains 70 to 75% of water. Such sludge has solids content that should, theoretically, produce more than enough heat necessary for evaporating the moisture content. However, though it appears to be theoretically possible to burn or dry-distill (the latter case includes effective use of the heat generated by fixed carbon) without requiring another heat source, the properties of the solids content may not permit the generation of so great an amount of heat, and in practice, an auxiliary fuel such as heavy oil has been necessary.